Acta crystallographica Section B, Structural science, crystal engineering and materials最新文献

CRYSP has been developed as a crystallographic tool for the construction and visualization of crystal shapes. The input parameters for software are crystal structure files, Miller indices, and corresponding minimum surface energies. A graphical user-friendly interface is provided, along with automatic conversion from crystallographic space groups to point groups, simplifying the input of interfacial energies and their orientations. The algorithm of Wulff construction, as described in a research paper on the SOWOS software, has been modified to include a cleavage option, enabling the identification of very small facets, short edges, and nearly coincidence vertices. This enhancement allows the construction of crystal shapes both in natural habits and on planar substrates, the latter corresponding to the Winterbottom construction. Visualization in pseudo-color is provided, including facet indices and quantitative parameters such as edge length, facet area, and crystal volume. The software also supports morphologies associated with non-crystallographic point groups, e.g. icosahedral symmetry. CRYSP serves as a versatile tool for crystallography, nanostructures and any other field where crystal facets are involved.

The newest three members of the Editorial Board of Acta Crystallographica Section B are introduced.

Single crystals of lacunary apatite structure-type compound Pb₄Na(PO₄)₃ were prepared with a flux/solid-state-reaction technique and consecutive melt-growth to examine spatial distribution and stereochemical activity of the 6s² lone electron pair of Pb²⁺ using X-ray diffraction. The target compound crystallized in space group P6₃/m with unit-cell edge lengths a = 9.7345 (12) Å and c = 7.2130 (18) Å without any indication of configurational ordering of Pb²⁺ and Na⁺ at the crystallographic A1 site. The anion channel running through the structure was confirmed as vacant. Residual density attributable to the deformed 6s² electron cloud was found 0.6 Å apart from the A2-site position on the A2 triangle normal to c. The lack of a channel-site anion induced shrinkage of the unit cell and the O3 trigonal antiprism in the xy plane, and an increase in the twist angle of the A1O₆ trigonal metaprism compensated for the shrinkage of the latter to keep the volume of the A1O₉ coordination polyhedron constant. Systematic comparison of the size of the A2 triangle in Pb₄Na(PO₄)₃ and other apatite-type compounds indicates no contribution from the 6s² electron orbital on the size of the A2 triangle and limited space-filling ability of the orbital. A2 cations are attached on the periphery of a large void formed by the in-plane distortion of the hexagonal close packed arrangement of (BO₄)^3- complex anions. In other words, a face-sharing array of A2 octahedra was inserted `as a tube' through the framework. The sizes of A1O₉ and BO₄ polyhedra and their framework define the maximum size of the A2 triangle, while the triangle can easily be shrunk by attraction from an anion, such as F^-, in the channel.

1,1'-(3,6-Pyrazabolyl)ferrocene [Fc(BHpz)₂] and the corresponding ruthenocene [Rc(BHpz)₂] crystallize as order-disorder (OD) structures with layers of Pma(m) symmetry. Since the m_[100] reflection and the a_[010] glide reflection planes of adjacent layers do not overlap, given one layer, the adjacent layer can be placed in four distinct, but geometrically equivalent, positions. There are accordingly four polytypes of a maximum degree of order (MDO). One analyzed Fc(BHpz)₂ crystal was composed of a mixture of the MDO₁ polytype in four distinct orientations and the MDO₃ polytype. A second crystal was essentially a single crystal of one out of two orientation of MDO₃. In two analyzed crystals of Rc(BHpz)₂, the MDO₁ polytype (P1) was the major polytype and was observed in four or two orientation states, respectively. Pronounced diffuse scattering is attributed to a complex disorder, which cannot be explained by simple growth models. One Rc(BHpz)₂ crystal features additional peaks in the diffraction pattern attributed to fragments of MDO₃.

MgO single crystals with diameters between 3.5 and 5 mm and lengths up to 40 mm were grown by the optical floating zone technique (OFZ). Despite challenging material properties such as the high melting point of 2825°C, very high evaporation rate and perfect {100} cleaving characteristics, crack-free crystals were grown at high growth rates exceeding 40 mm h^-1 and at high thermal gradients. Chemical investigations revealed that the OFZ technique is suitable for the preparation of substrate crystals with a purity of 5N to facilitate the development of novel demonstrator devices based on epitaxially grown thin films. The achieved purity level is improved by more than one order of magnitude if compared to commercial MgO substrate single crystals graded as high purity.

Single crystal specimens of Fe_2.992O₄ (magnetite), Fe_3-x-yMn_x□_yO₄ (x ≤ 0.980) and Fe_3-x-yNi_x□_yO₄ (x ≤ 0.513, □ denotes point defects) are prepared using a floating-zone technique, and changes in their structural parameter values with x are examined at room temperature. Preferences of Mn, Ni and point defects at A, B and B sites, respectively, are confirmed by single-crystal X-ray diffraction experiments, while preference of Mn at the A site is not perfectly accomplished in Fe_2.010Mn_0.980O₄. Mean-square displacements of atoms along the 3 axis in [111] are peculiarly large at the B site in Fe_2.992O₄ and the displacement decreased smoothly in both series, to nearly half in Fe_2.00Mn_0.980O₄, with increasing amount of heteroatom. On the other hand, displacements normal to the direction show only slight convexity with x due to coexistence of the heteroatom. As a result anisotropy in displacements (dominant in [111] at x = 0) is inverted at x = 0.3 in FeMn series and would expectedly be inverted at x ≃ 0.55 in FeNi series. In spite of different locations of heteroatoms and slightly different inversion points on anisotropy, changes in mean-square displacements at the B site in [111] in these series are found on similar lines with changing amounts of heteroatom. In other words, the amount of this displacement is a function of the amount of Fe²⁺, or remnant electron from the itinerant-electron point-of-view, on the B-site substructure in these compounds. This characteristic lattice mode on the B-site substructure could be interpreted as an average of local distortion of the substructure due to `trimeron' [Senn et al. (2012). Nature, 481, 173-176] and some other modes such as distortion in 〈001〉 [Siratori & Kino (1980). J. Magn. Magn. Mat. 20, 87-90], which moves in the high-temperature structure.

The minerals mcgovernite and carlfrancisite possess an extraordinary rhombohedral unit cell [mcgovernite: a = b = 8.206 Å and c = 204.118 Å, with the complex formula unit M²⁺₁₉Zn₃(OH)₂₁(AsO₃)(AsO₄)₃(SiO₄)₃ (M = Mn, Mg, Zn); carlfrancisite similar]. Hawthorne [(2018), Mineral. Mag. 82, 1101-1118] reported a single-crystal study using a centrosymmetric model (R3c) containing disorder on three cationic sites and an As^III lone-pair site for both mcgovernite and carlfrancisite. A solution of the structure of mcgovernite from high-resolution synchrotron powder diffraction data suggests a reinterpretation of the crystal structures of mcgovernite and carlfrancisite as noncentrosymmetric R3c with ordered planar defects which allows for merohedral twinning.

Magnetic axial and polar (Dirac) nickel multipoles contribute to resonant X-ray Bragg amplitudes in a symmetry-informed analysis of monoclinic Li₂Ni₃P₄O₁₄ presented for future diffraction experiments. Magnetic long-range order below a temperature of ≃ 14.5 K can be viewed as a two-dimensional trimerized antiferromagnet with Ni ions in two Wyckoff positions in the centrosymmetric (1) magnetic space group P2₁/c. It permits the coupling to circular polarization in the primary X-ray beam, unlike the corresponding diffraction by an antiferromagnet characterized by anti-inversion (1') and a linear magnetoelectric effect, e.g. historically significant chromium sesquioxide (Cr₂O₃) and Cu₂(MoO₄)(SeO₃) [Lovesey & van der Laan (2024). Phys. Rev. B 110, 174442]. The space group is inferred from neutron Bragg diffraction patterns, without an allowance for permitted Dirac dipoles (anapoles) and quadrupoles [Chikara et al. (2025). Phys. Rev. B 112, 014438].

Charge density and local electrostatic and quantum kinetic electron forces acting on the bound atoms in [Co(NH₃)₅NO₂]ClNO₃ (nitro isomer) and [Co(NH₃)₅ONO]ClNO₃ (nitrito isomer) were studied to elucidate to the role of the crystalline environment in the intramolecular nitro-nitrito linkage photoisomerization. Quantum crystallography and orbital-free DFT approaches were applied. In the more stable nitro isomer, the -NO₂^- group forms two hydrogen bonds with the NH₃ ligands, while in the nitrito isomer the -ONO^- group is not involved in any hydrogen bonds, however, it forms van der Waals contacts with surrounding atoms. No bond paths in the electron density were found between the anions NO₃^- and Cl^-, which were previously supposed to play an important role in photoisomerization. Still, these anions do interact with each other in both isomers via an indirect mechanism involving H atoms of -NH₃ ligands. Whereas there is no direct electrostatic interaction between the anions in the nitro isomer, the part of electrons belonging to the Cl^- anion in the nitrito isomer is pulled towards the nucleus of an oxygen atom of the NO₃^- anion, creating a favorable condition for direct interaction between anions through corresponding local electronic forces directed to the nuclei. The link of cation/anion atomic basin volumes relationship and nature of the intermolecular interactions is established.

Thermal evolution of the unit-cell parameters a, b and c as well as the unit-cell volume V of R₅Pt₂In₄ (R = Tb-Tm) is derived from the neutron powder diffraction data. For all investigated compounds, the above mentioned parameters show a noticeable change in vicinity of the critical temperature of the magnetic order. At lower temperatures, additional anomalies are found for R = Tb-Er. These anomalies are related to the magnetic phase transitions of the order-order type originating from appearance and/or rapid increase of the magnetic rare earth moment at one of the 4g Wyckoff sites. The above mentioned results indicate presence of the magnetoelastic effect in the investigated intermetallics. Based on the experimental data, the product of compressibility and magnetoelastic coupling in R₅Pt₂In₄ (R = Tb-Tm) is found to be 0.014 (2)%·μ_B^-2.